The latest research quantifies how much smoking contributes to sudden heart-related death and how quitting can potentially erase that risk.

Smoking is a well-known risk factor for heart disease; lighting up can damage blood vessels with the buildup of dangerous plaque that can raise blood pressure and eventually rupture, triggering heart attacks. But how quickly does the harm occur?

Researchers led by Dr. Roopinder Sandhu at the University of Alberta’s Mazankowski Heart Institute, in Canada, report in the journal Circulation: Arrhythmia and Electrophysiology that women who currently smoke are nearly two and a half times more likely to die from sudden cardiac death — a loss of heart function and the largest cause of natural death in the U.S. — than those who never smoked.

In most cases, those fatal heart attacks occur in people who do not have a history of heart disease or heart failure. In the study, Sandhu and his colleagues set out to document in more detail the relationship between the number of cigarettes smoked, the duration of smoking and the impact of quitting smoking on the risk of sudden cardiac death — particularly among women and patients without known heart disease.

The researchers turned to the Nurses’ Health Study, a 30-year survey of the health outcomes of 101,018 women ages 30 to 55. None of the women had documented heart disease at the start of the study, and they reported on whether they currently smoked or smoked in the past, and if they did, when they started lighting up. Current smokers also provided the number of cigarettes they smoked daily: 1 to 14 (which the researchers considered light to moderate smoking), 15 to 24 (which they labeled as moderate), or more than 25 (considered to be heavy smoking). Past smokers also reported the age at which they started smoking and the number of cigarettes they smoked before they quit.

Even after the scientists adjusted for factors that could affect heart disease, such as age, history of diabetes, hypertension, high cholesterol, weight, aspirin use, multivitamin use, menopausal status and postmenopausal-hormone use, the relationship between any smoking and an increased risk of sudden heart death remained. Over 30 years, 351 women died of sudden heart attacks. Among them, even women who smoked the least — 1 to 14 cigarettes — were nearly two times more likely than nonsmokers to be at risk for sudden cardiac death. Women who smoked 25 or more cigarettes were more than three times as likely to die suddenly. Moreover, for every five years that a woman continued smoking, her risk of dying from a heart attack increased by 8%.

As sobering as the results are, the researchers found some positive trends as well. For women with heart disease who stopped smoking, their risk of sudden death decreased to that of a nonsmoker’s level within 15 and 20 years — meaning that whatever harm lighting up does to the heart is reversible to a certain extent.

That may explain why a separate study found that quitting might add 10 years to female smokers’ lives; a survey of more than a million women in the U.K. reported that smokers who kicked the habit virtually eliminated their threefold increased risk of dying prematurely.

The authors acknowledge that one of the drawbacks to their analysis is the lack of diversity in the study population — the women were overwhelmingly Caucasian and came from similar sociodemographic backgrounds, so it’s not clear whether the same trends are occurring in different populations, including men. The authors also did not have enough data about the severity of heart events to determine whether quitting smoking was associated with heart attacks that were less likely to be fatal.

But because the heart attacks occurred in women with no history of heart disease, the results highlight the importance of educating women about the risks of smoking and the benefits of quitting. “Sudden cardiac death is often the first sign of heart disease among women, so lifestyle changes that reduce that risk are particularly important,” Sandhu said in a statement. “Quitting smoking before heart disease develops is critical.”